The invention relates to a method of producing brushes by connecting plates of a plastic material, having each tufts of brush bristles attached thereto and projecting from a first face, to an attachment surface portion of a brush body made of plastic, in particular the same plastic, by means of ultrasonic welding or gluing.
It is known in brush making to attach tufts of bristles to carrier plates which are then attached to a brush body. The attachment of the carrier plates to the brush bodies can be done by welding, in particular when the carrier plates and the brush bodies are made of the same plastic material. At the junction between the carrier plate and the surface of the brush body a gap may be produced which is undesirable both for reasons of aesthetics and also for reasons of hygiene.
The invention provides a method of reliably connecting the carrier plate to the brush body without an undesirably large gap remaining between the carrier plate and the brush body.
In accordance with a first aspect of the invention, the plastic materials of the plate and the brush body are connected by ultrasonic welding. Formed on the peripheral rim of the plate is an edge facing the brush body and acting as an energy concentrator in ultrasonic welding. Welding is therefore effected with high precision, so that also in mass production such as in the case of toothbrushes, for example, the plate is attached to the brush body with a precise fit. The edge preferably tapers toward the brush body. In an advantageous embodiment of the method the brush body is provided with a recess into which the plate can be inserted with a precise fit. The gap remaining between the outer edge of the plate and the rim of the recess will then be very small and barely perceptible.
In this embodiment of the method, the edge engages the bottom of the recess by its tapered end, so that the weld joint is produced at the bottom of the recess. The welding process is further assisted by a pressing means which presses the plate against the bottom of the recess of the brush body.
Preferably, an extension projecting beyond the recess of the brush body is formed at the peripheral rim of the plate. This extension may extend over the entire periphery of the plate or only over a part thereof, preferably over that part which extends as far as into the neck piece of the brush body in the case of a toothbrush. Bending loads occur at this point which cause any gap that possibly remains between the plate and the brush body to be opened when the head of the toothbrush is bent back in use. This extension, too, is preferably provided with a tapered edge which faces the brush body and acts as an energy concentrator in ultrasonic welding.
Any gap that may still be left between the plate and the brush body may be closed by a finishing treatment, in particular by filling it with a suitable plastic mass. More particularly, the brush body with the plate already fitted therein may be placed in an injection mold which is used to apply a molding over the gap so as to completely fill it and close it.
In an alternative embodiment of the method according to the invention, the brush body is provided with a recess into which the plate is inserted with a precise fit and attached there by means of an adhesive. Also in this embodiment, any gap possibly left between the plate and the brush body may be closed by molding in an injection mold.
In a further embodiment of the invention, the plates are attached to the brush bodies using a combination of ultrasonic welding and glueing. In particular, the load-bearing fastening of the plate may be performed by welding it to the bottom of the recess of the brush body, whereas the adhesive is introduced into the gap remaining between the plate and the brush body and fills the same.